What Is JPG? JPEG Format Explained

JPG (or JPEG, short for Joint Photographic Experts Group) is the most widely used photo format: it saves an image with lossy compression, dropping fine detail the eye barely notices, so the file is several times smaller. Every phone, computer and browser opens it, and Amazon UK recommends it for product images.

Below: our test of one packshot saved 11 ways, and the steps to open a JPG file and convert photos to JPG.

JPG meaning and full form

JPG stands for Joint Photographic Experts Group, the ISO and IEC committee that wrote the standard (“Joint” refers to its work with the ITU, jpeg.org). Work began in 1986 (jpeg.org). The standard was approved as ITU-T T.81 on 18 September 1992 and as ISO/IEC 10918-1 in 1994.

See also: How to read a photo histogram

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Strictly speaking, JPEG is the compression method, and the file we call “a JPEG” follows the JFIF format (part 5 of the standard). In practice .jpg and .jpeg are exactly the same format. The shorter spelling most likely survives from MS-DOS, which allowed only three characters in a file extension.

JPG is a raster format, not a vector one

A JPG stores a fixed grid of pixels: a 2000 × 2000 px photo is 4 million points, each with three colour components of 8 bits (MDN). Enlarged beyond that, it turns soft. Logos and icons that must scale without loss are saved as vector graphics in SVG.

Specifics of the JPG format: what it can and cannot do

• Colour: 8 bits per component, about 16.7 million colours. Heavy editing of a smooth sky can show banding.
• Transparency: none. A transparent PNG background turns into a solid colour.
• Size: up to 65,535 × 65,535 px.
• Compatibility: every version of Chrome, Edge, Firefox, Opera and Safari (MDN), and every system and image editor.

Where JPG is used

1. Photography. Cameras save JPG, or RAW and JPG together. The iPhone is the exception: Apple recommends HEIF, so JPG has to be switched on (see below).
2. Websites and online shops. A smaller file loads faster, so packshots on a white background usually go to the shop as JPG.
3. Print and delivery. Photo labs accept high-quality JPGs, and studios deliver finished images as JPG because anyone can open them.

See also: WebP: a short guide for business

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How JPG compression works

JPG uses a lossy algorithm that removes the information least important to the eye, in four steps:

1. Colour conversion from RGB to YCbCr: brightness and colour are stored separately, colour usually at a lower resolution, because the eye sees its detail less well.
2. 8 × 8 px blocks and a discrete cosine transform (DCT), which splits each block into low and high frequencies.
3. Quantisation: fine detail is rounded more coarsely than smooth transitions. This is where the loss happens.
4. Entropy coding, which packs the result into the file without further loss.

The “quality” slider is sometimes shown as a percentage, but it is not a percentage of quality. It sets how coarse the rounding in step 3 is, and every program calculates it differently, so “quality 85” in two programs gives two different files: in our test 103.6 kB and 74.2 kB (screenshot below).

Here is the same landscape saved at quality 100 and quality 5. In a small preview even 5 is still readable.

Pros and cons of JPG compression

Pros:

• Small files: in our test 7.5 times smaller than a PNG of the same photo.
• Every browser, system and image editor opens it.

Cons:

• The loss is permanent and adds up every time you save again after editing.
• Heavy compression brings 8 × 8 px blocks, smeared textures and specks around lettering.
• No transparency and no animation.

Lossy vs lossless compression

Lossy compression (JPG) permanently discards some data. Lossless compression (PNG, TIFF, lossless WebP) restores every pixel. The JPEG standard has a lossless mode (jpeg.org), but an ordinary .jpg file is lossy. JPG is enough for the web and for shops, while for print, archiving and editing you keep a lossless original: the RAW file, TIFF or PNG.

Pro tip: editing a photo several times? Work on a TIFF or PSD copy and save the finished file as JPG once. Every “open, fix, save as JPG” round compresses the image again.

Test: the same photo as JPG, PNG, WebP and AVIF

JPG at quality 85 weighed 103.6 kB. WebP with the same similarity to the original weighed 46.6 kB (55% less), AVIF 29.8 kB (71% less) and lossless PNG 777 kB, 7.5 times more. The photo is our packshot of an Urbannote candle at 2000 × 2000 px, and we measured similarity with SSIM on the product itself (1 = identical).

Saved as	File size (vs JPG 85)	Product SSIM	Paper texture
JPG 95	186.8 kB (+80%)	0.988	as original
JPG 85	103.6 kB	0.975	68%
JPG 75	80.5 kB (-22%)	0.969	56%
JPG 60	66.1 kB (-36%)	0.963	50%
JPG 30	50.7 kB (-51%)	0.948	8 × 8 px blocks
PNG	777.0 kB (+650%)	1.000	lossless
WebP lossless	501.6 kB (+384%)	1.000	lossless
WebP 85	46.6 kB (-55%)	0.976	63%
WebP 80 (default)	39.7 kB (-62%)	0.973	53%
AVIF 60	29.8 kB (-71%)	0.975	45%
AVIF 75 (default)	46.0 kB (-56%)	0.981	86%

“Paper texture” is the fine grain of the label paper, measured as brightness variation in a 60 × 60 px patch (original = 100%). At JPG 30 the blocks add their own variation, so the figure means nothing there. The numbers in the names are Pillow quality settings, and the JPG, WebP and AVIF scales are not comparable.

What the test shows

• JPG 80-85 is a sensible choice for a shop. Going from 95 to 85 saves 83 kB, from 85 to 60 only 37.5 kB more, and that step eats the paper texture.
• WebP and AVIF match JPG 85 in a file 2 to 3.5 times smaller, but smooth textures more. The default AVIF 75 beat JPG 85 at less than half the size.
• PNG does not pay off for photos: 777 kB with no visible benefit, while JPG 95 scores 0.988 at a quarter of the size.
• Check the background colour at low quality. JPG 60 shifted the light grey background by 3 levels in red and blue, and JPG 30 turned it neutral grey.

Pro tip: size first, quality second. Our 6000 × 6000 px source, an almost lossless JPG, weighed 4.98 MB. Reduced to 2000 px as JPG 85 it weighs 103.6 kB, 48 times less. See how to change the size of an image for free.

Test method and its limits

• Photo: packshot of the Urbannote Towarzyski Wrocław 190 g candle (Canon EOS R, processed file: JPG 6000 × 6000 px, almost lossless, sRGB), reduced with Lanczos to 2000 × 2000 px as the reference.
• Tools: Python 3.14 and Pillow 12.3.0 (libjpeg-turbo 3.1.4.1, libwebp 1.6.0, libavif 1.4.2 with aom 3.14.1), Windows 11, 28 October 2026. JPG with optimised coding and 4:2:0 colour, WebP method 6, AVIF speed 4, no EXIF or ICC; 1 kB = 1000 bytes.
• Measure: SSIM on luminance in a 720 × 940 px box around the product, because the flat background inflates the score. WebP and AVIF are the lowest quality with SSIM at least equal to JPG 85.
• Limits: one photo and one library; other encoders give other numbers, and SSIM does not replace the eye. JPEG XL was not tested, because Pillow 12.3 cannot save it.

How to open a JPG file and convert photos to JPG

You can open a JPG without installing anything: in a web browser (drag the file into the window), in the Photos app on Windows, in Preview on a Mac and in your phone’s gallery.

Why a JPG file will not open

• It is not a JPG. A HEIC or WebP photo renamed to .jpg is still HEIC or WebP.
• A codec is missing. Windows Photos opens iPhone HEIC photos only with the HEIF and HEVC extensions.
• The file is damaged, for example by an interrupted download. Download it again.

Windows 11: HEIC, PNG and WebP to JPG

1. For HEIC install HEIF Image Extensions (free) and HEVC Video Extensions (£0.79 in the UK Microsoft Store on 29 October 2026). Microsoft says you need both, even for photos. Then restart Photos.
2. Open the image in Paint and save it under a new name with JPEG as the file type (Paint help). A transparent background turns into a solid colour.

Mac, iPhone and Android

• Mac: open the file in Preview, choose File > Export, pick JPEG in the Format menu and set the quality (Preview User Guide).
• iPhone: Settings > Camera > Formats > Most Compatible saves new photos as JPEG. When you copy photos to a computer by cable, the iPhone may convert HEIC to JPEG itself, unless you tap Keep Originals in Settings > Apps > Photos (Apple Support).
• Android: names vary by brand. On the Galaxy A16 to A56, a High efficiency pictures switch in the camera settings saves HEIF (Samsung help). Pixel saves JPG, and its RAW + JPEG option adds a RAW file.

Need a document rather than an image? Our free JPG to PDF converter works in the browser in both directions, and the guide to PDF to JPG converters shows other free ways to convert.

Tools and programs that support JPG

• Adobe Photoshop: full editing with layers, masks and colour correction.
• GIMP and Paint.NET: free alternatives; Paint.NET is the simpler of the two.
• Canva and other photo editing apps: templates and quick fixes.
• Squoosh: compression in the browser with a before-and-after view.

Advice for photographers and graphic designers

1. Match the quality to the destination: JPG 80-85 for websites and shops, 90-95 for print.
2. Edit the original. Do retouching and colour correction on RAW, TIFF or PSD. A JPG cannot give back what compression removed.
3. Check at 100% zoom. Label lettering, fabric texture and product edges show artefacts first.

JPG vs other graphic formats

Format	Compression	Transparency and animation	Best for
JPG	lossy	no, no	photos, shops, sharing files
PNG	lossless	yes, animation only in the APNG variant	logos, screenshots, graphics with a transparent background
WebP	lossy and lossless	yes, yes	websites
AVIF	lossy and lossless	yes, yes	websites, the smallest files
GIF	lossless, up to 256 colours	yes (one transparent colour), yes	simple animations
TIFF	usually uncompressed or lossless	yes (rarely used), no	print, archive

When to use JPG, PNG or WebP

• JPG: when everyone has to accept the file: a shop, a marketplace, a print lab, a client on an old laptop. The natural choice for product photos.
• PNG: for transparency or sharp edges: logos, graphics with text, screenshots. Not for photos: in our test it was 7.5 times heavier than JPG 85.
• WebP: for your own website. Google says lossy WebP is 25-34% smaller than JPEG at the same SSIM; in our test, on one photo, it was 55%.
• GIF and TIFF: GIF has only 256 colours and is still used for simple animations; TIFF keeps full quality and layers for print, in files several times larger.

Each format handles photo compression differently, but none fixes a weak photo: compression cannot add sharpness or light, only take them away. If you need packshots that look good in any format, get in touch.

See also: Adobe Express: our review

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AVIF and JPEG XL: the successors to JPG in October 2026

1. HEIF (.heic files) uses the HEVC codec. Apple recommends it on iPhones, because the files take less space than JPEG (Apple Support).
2. AVIF is an image saved with the AV1 video codec (AOMedia specification 1.0.0 of 19 February 2019). Like WebP, caniuse marks it as widely available across major browsers, and in our test it gave the smallest file.
3. JPEG XL (ISO/IEC 18181) comes from the JPEG committee. It can losslessly repack an old JPG into a smaller file and restore it bit for bit (jpeg.org).

JPEG XL on 29 October 2026: Chrome supports it by default from version 155 (Chrome blog, 6 October 2026), Firefox from version 158 of 13 October 2026 (MDN) and Safari from version 17 (WebKit), though Safari has no animation or progressive loading. caniuse puts support at 59.77% of users worldwide (42.84% full, 16.93% partial), based on September data, in which the new desktop versions of Chrome and Firefox barely count yet.

AVIF and JPEG XL also support HDR, and websites serve them with a JPG or WebP fallback, as MDN recommends. JPG will remain the exchange format of the digital imaging world for a long time, because every shop, print lab and client accepts it.

See also: Resize an image online

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Which format for shop and marketplace photos

• Amazon UK: JPEG, TIFF, PNG or non-animated GIF, with JPEG recommended. The longest side must be 500-10,000 px, and 1,000 px or more enables zoom. RGB colour mode is preferred, and the main image needs pure white, RGB 255, 255, 255 (Amazon UK product image guide).
• eBay UK: at least 500 × 500 px, about 1600 × 1600 px recommended, files up to 12 MB (eBay help). Fees and tips are in our eBay UK guide.

At marszalstudio we deliver packshots as JPG 2000 × 2000 px, 72 DPI, RGB, a file Amazon and eBay accept without conversion, from €9 net per photo. PNG without background, 6K resolution and a custom size are add-ons at €3 per photo, listed in our product photography pricing.

Frequently asked questions about JPG

Summary

• JPG is a lossy photo format from 1992 that every device opens; .jpg and .jpeg are the same thing.
• For shops and websites, reduce the pixel size and save JPG at quality 80-85. Lower, the product loses texture.
• On your own site, WebP and AVIF give files 2 to 3.5 times smaller. Keep a lossless original and save the JPG once, at the end.